1. Technical Field
This invention relates to circuitry for receiving data from a transmission line and, more particularly, to such an electrical input buffer circuit that may interface an automotive control module and remote electronic drive circuitry.
2. Discussion
Ignition systems for automotive vehicles commonly employ an engine control module (ECH) and remote electronic ignition drive circuitry provided in an ignition module The function of the ignition drive circuitry is to provide switching and current limit control of ignition coil currents which are fed to the ignition coil for purposes of producing spark in the cylinders of the engine. In automotive vehicles, the ignition drive circuitry is commonly located in the immediate proximity of the ignition coil at the engine.
The drive voltage that commands the ignition system "on" has generally been transmitted on a single wire which is referenced to the vehicle ground. One problem that arises with conventional approaches is that the ignition module may be affected by noise since the ignition module is often located very close to the spark plugs on the engine The ignition system conducts high currents in the ignition coils in order to provide enough energy to create the necessary spark These high ignition currents can travel through conductors in the ignition module and out a wiring harness back to a ground reference This may cause the development of some undesirable induced voltage drop across the ground reference wires. Ground variations in the electrical interface between the engine control module and the ignition module due to these high currents in the ignition coil can result in ground differences of greater than two volts. As a consequence, the single-ended drive signal may become less attractive since the input voltage is consumed by noise induced signals appearing across the ground reference wire. In effect, the ground reference rises above the signal of the ground that the engine control module is utilizing to provide the drive signal.
To eliminate noise induced on the ground line, separate reference voltage lines can be used to set the ground for each individual ignition module. However, the presence of separate reference voltage lines requires additional wiring which increases the wiring costs and requires added IC input area. In addition, if the voltage on the transistors and resistors is below the substrate voltage of the IC, the required isolation between the ground reference and the IC may dissipate. It is therefore desired to have an integrated circuit device that can operate much below ground.
Another problem that arises with the integrated circuitry is that the circuitry is required to operate from temperatures as low as minus forty degrees (40.degree.) celsius to temperatures as high as one-hundred-sixty-five degrees (165.degree.) celsius. Despite variances within such a large temperature operating range, it is generally required that the voltage threshold for the integrated circuitry should not deviate with temperature changes. In order to meet this temperature requirement, the circuitry must provide temperature compensation since many of the parametrics of the integrated circuitry change with temperature. For example, resistors are known to vary in resistance as temperature changes. Similarly, the base-to-emitter voltage on transistors generally swing as the temperature changes.
One example of an input buffer circuit that provides hysteresis with temperature compensation is described in U.S. Pat. No. 5,121,004, entitled "Input Buffer with Temperature Compensated Hysteresis and Thresholds Including Negative Input Voltage Protection", issued on Jun. 9, 1992. The aforementioned U.S. patent is owned by the Assignee of the present application and is incorporated herein by reference. The input buffer circuit of the above-identified patent utilizes first and second temperature dependent currents, one having a negative temperature coefficient and the other having a positive temperature coefficient such that the sum effect of the temperature coefficient on the circuit is substantially zero. The above approach receives a single-ended input and utilizes local grounds as the reference. While the above approach provides adequate hysteresis and temperature compensation, that approach is limited in that it may not be able to detect the input signal when the reference is below the local ground. This is increasingly significant for ignition systems which transmit higher currents and are located very close to the engine.
It is therefore desirable to provide for an electrical input buffer circuit that is capable of receiving transmitted data from a transmission line and provides an output signal despite the presence of noises it is particularly desirable to provide for an electrical input buffer circuit which may interface between an automotive engine control module and a remote electronic ignition drive circuit that is located near the automotive ignition coils and the engine. It is further desirable to provide for such a circuit implemented in integrated circuitry that is capable of operating above and below ground. It is also desirable to provide for such an integrated circuit that compensates for temperature deviations within the integrated circuitry.